In a magnetic resonance imaging apparatus, an echo signal obtained at a reception coil is transmitted from a coil side unit to a system side unit. In this case, a digital signal obtained by digitalizing the echo signal is wirelessly transmitted, whereby the reception coil is made to be wireless. This system is known from U.S. Pat. No. 5,384,536 (hereinafter referred to as Reference 1).
When the echo signal is digitalized in this manner, it is necessary to use a clock signal having the same frequency in transmission processing and reception processing of the digital signal. If a frequency shift occurs in the clock signal, the echo signal deteriorates, and accuracy of an image reconstructed from this echo signal might lower.
In Reference 1, a first clock signal which is used for the reception processing is wirelessly transmitted as a reference signal. On the basis of this reference signal, a second clock signal is generated which is used in the transmission processing.
In a case where the system of Reference 1 is used, the second clock signal can accurately be synchronized with the first clock signal, if the reference signal is transmitted without any deterioration. However, usually in the wireless transmission, ambient electric waves function as interference waves, and hence the deterioration occurs. For example, a 2.4 GHz band (2400 to 2483.5 MHz) can be utilized without any restriction of a band width and a modulation system, if it does not exceed a regulated electric intensity. The regulated electric intensity is 50 mV/m in the United States and 10 mW in Europe at a distance of 3 m. The above frequency band is sufficiently distant from the frequency (about 64 MHz) of the echo signal, and includes a frequency which permits easy diode detection. Accordingly, the above frequency band is considered to be suitable as a carrier frequency of the clock signal. However, the above frequency band is used in wireless communication systems such as wireless LAN and Bluetooth (registered trademark), and in various use applications as an ISM band. Hence, the electric waves used in these use applications might function as the interference waves.
In view of such situations, it has been desired to decrease influence of the interference by the other electric waves.